Harbors throughout the United States require periodic dredging to maintain sufficient draft depth for shipping. The dredge spoil produced by this operation is loaded into bottom dump barges and transported out to sea to underwater dredge disposal sites which have been identified by the U.S. Army Corps of Engineers.
At the disposal site the dredge spoil material is simply dumped from the barge and allowed to settle to the bottom of the sea at a depth ranging from 150 to 200 feet. This procedure creates large domes of dredge spoil material which range from 1000 to 2300 feet in diameter. The dredge spoil material oftentimes includes contaminated material which is potentially harmful to the environment. A solution is presently being sought to develop ways of capping these domes to prevent migration of the contaminated material to the surrounding ocean beds and water.
A proposed solution to this problem is the use of a concrete mass to cap the domes of contaminated material.
There is currently a concrete revetment system on the market, sold under the name of ARMORFLEX and disclosed in U.S. Pat. No. 4,370,075. In this system, a plurality of individual concrete blocks are cast with horizontally and vertically oriented holes. After the blocks have cured, they are then moved to an assembly area where they are positioned into their final configuration by hand. This is then followed by the threading of steel cables through the horizontally oriented, pre-formed holes in each concrete block to tie the entire panel together. The panels are then lifted from both ends of the steel cables by a sling system and placed in a position of use. The vertically oriented holes that are cast into the concrete blocks are for soil filling to allow for revegetation through the vertically oriented holes.
The two cables passing through the horizontally oriented pre-formed holes allow movement of each block unit. Repeated abrasion of the cables under wave action can cause eventual failure of the cable system. Should this occur the entire panel configuration would be in jeopardy. To prevent this occurring, the individual concrete blocks are designed based upon the expected wave forces. The main component of this design is the weight and size of each individual concrete block.
In another system, sold under the name ARMORFORM and disclosed in U.S. Pat. Nos. 4,449,847 and 4,502,815, a high strength fabric bag system is pumped full of concrete grout after the bag has been placed in its final position of use. This system is limited to revetment applications and cannot be economically placed in deep water.
Each of these systems has one thing in common, that is, its size is relatively small and placement is accomplished by either installation in place or by lifting small pre-assembled units. The size of these known concrete structures is on the order of twenty feet long by six-to-ten feet wide. Such concrete structures simply cannot accomplish the goal of efficiently capping the domes of contaminated dredge material.